I've always liked Google Video's interface, even though is not as community-focused as YouTube's interface. Now that most video content will go to YouTube and Google Video will become a search engine, those who prefer its layout have a way to make YouTube more like Google Video.
This Greasemonkey script expands the video to occupy more space and puts the comments next to the related videos and the video description in a small sidebar. To install the script, you need to have Firefox and the Greasemonkey extension.
For a YouTube look in Google Video, you don't need a script.